Auxiliary power supply circuit and power supply device

Abstract

An auxiliary power supply circuit connected to a switching circuit in which a high-withstand-voltage transistor and a low-withstand-voltage transistor are connected in series includes a rectification element and an auxiliary power supply capacitor. A connection node between the high-withstand-voltage transistor and the low-withstand-voltage transistor is connected to an anode of the rectification element. A cathode of the rectification element is connected to a positive electrode of the auxiliary power supply capacitor. A negative electrode of the auxiliary power supply capacitor is connected to a reference terminal of the low-withstand-voltage transistor.

What is claimed is: 
     
         1 . An auxiliary power supply circuit connected to a switching circuit,
 the switching circuit including a high-withstand-voltage transistor and a low-withstand-voltage transistor connected in series, the high-withstand-voltage transistor being disposed on a high-voltage side, the low-withstand-voltage transistor being disposed on a low-voltage side,   the auxiliary power supply circuit comprising a rectification element, and an auxiliary power supply capacitor,   wherein a connection node between the high-withstand-voltage transistor and the low-withstand-voltage transistor is connected to an anode of the rectification element,   a cathode of the rectification element is connected to a positive electrode of the auxiliary power supply capacitor,   a negative electrode of the auxiliary power supply capacitor is connected to a reference terminal of the low-withstand-voltage transistor, and   a voltage at the connection node generated when the switching circuit operates is supplied to the auxiliary power supply capacitor.   
     
     
         2 . The auxiliary power supply circuit according to  claim 1 , further comprising an auxiliary-power-supply-capacitor Zener diode,
 wherein the auxiliary-power-supply-capacitor Zener diode has
 a cathode connected to the positive electrode of the auxiliary power supply capacitor, and 
 an anode connected to the negative electrode of the auxiliary power supply capacitor. 
   
     
     
         3 . The auxiliary power supply circuit according to  claim 1 , further comprising a smoothing capacitor, and an inrush-current limiting resistor,
 wherein the smoothing capacitor has
 a positive electrode connected to the cathode of the rectification element, and 
 a negative electrode connected to the reference terminal of the low-withstand-voltage transistor, and 
   wherein the inrush-current limiting resistor is interposed on a connection path between the cathode of the rectification element and the positive electrode of the auxiliary power supply capacitor.   
     
     
         4 . The auxiliary power supply circuit according to  claim 1 , further comprising a smoothing capacitor, and an LDO,
 wherein the smoothing capacitor has
 a positive electrode connected to the cathode of the rectification element, and 
 a negative electrode connected to the reference terminal of the low-withstand-voltage transistor, 
   wherein the LDO is interposed on a connection path between the cathode of the rectification element and the positive electrode of the auxiliary power supply capacitor, and   wherein the LDO has
 an input terminal connected to the anode of the rectification element, 
 an output terminal connected to the positive electrode of the auxiliary power supply capacitor, and 
 a reference terminal connected to the reference terminal of the low-withstand-voltage transistor. 
   
     
     
         5 . The auxiliary power supply circuit according to  claim 1 , further comprising a general auxiliary power supply,
 wherein the general auxiliary power supply has
 a positive electrode connected to the positive electrode of the auxiliary power supply capacitor, and 
 a negative electrode connected to the negative electrode of the auxiliary power supply capacitor. 
   
     
     
         6 . The auxiliary power supply circuit according to  claim 5 , wherein an output voltage of the general auxiliary power supply is lower than a voltage of the auxiliary power supply capacitor. 
     
     
         7 . The auxiliary power supply circuit according to  claim 1 , further comprising a startup circuit,
 wherein the startup circuit charges the auxiliary power supply capacitor before the switching circuit operates.   
     
     
         8 . The auxiliary power supply circuit according to  claim 1 , wherein
 the auxiliary power supply circuit is a gate-drive power supply circuit,   the auxiliary power supply capacitor is a gate drive capacitor,   the gate-drive power supply circuit further comprises a high-withstand-voltage-transistor gate drive capacitor, and   a voltage is supplied from the gate drive capacitor to the high-withstand-voltage-transistor gate drive capacitor.   
     
     
         9 . A power supply device comprising the auxiliary power supply circuit according to  claim 1 .